rcapd Operation Intervals

You can tune the intervals for the periodic operations performed by rcapd.

All intervals are specified in seconds. The rcapd operations
and their default interval values are described in the following table.

Operation

Default Interval Value in Seconds

Description

scan

15

Number of seconds between scans for processes that have joined or left
a project workload. Minimum value is 1 second.

sample

5

Number of seconds between samplings of resident set size and subsequent
cap enforcements. Minimum value is 1 second.

report

5

Number of seconds between updates to paging statistics. If set to 0, statistics are not updated, and output from rcapstat is
not current.

config

60

Number of seconds between reconfigurations. In a reconfiguration event, rcapadm reads the configuration file for updates, and scans the project database for new or revised project caps. Sending a SIGHUP to rcapd causes an immediate reconfiguration.

Determining rcapd Scan Intervals

The scan interval controls how often rcapd looks
for new processes. On systems with many processes running, the scan through
the list takes more time, so it might be preferable to lengthen the interval
in order to reduce the overall CPU time spent. However, the scan interval
also represents the minimum amount of time that a process must exist to be
attributed to a capped workload. If there are workloads that run many short-lived
processes, rcapd might not attribute the processes to a
workload if the scan interval is lengthened.

Determining Sample Intervals

The sample interval configured with rcapadm is
the shortest amount of time rcapd waits between sampling
a workload's usage and enforcing the cap if it is exceeded. If you reduce
this interval, rcapd will, under most conditions, enforce
caps more frequently, possibly resulting in increased I/O due to paging. However,
a shorter sample interval can also lessen the impact that a sudden increase
in a particular workload's physical memory usage might have on other workloads.
The window between samplings, in which the workload can consume memory unhindered
and possibly take memory from other capped workloads, is narrowed.

If the sample interval specified to rcapstat is shorter
than the interval specified to rcapd with rcapadm,
the output for some intervals can be zero. This situation occurs because rcapd does not update statistics more frequently than the interval
specified with rcapadm. The interval specified with rcapadm is independent of the sampling interval used by rcapstat.